1. Field of the Invention
The present invention relates to a reaction force apparatus for assisting a vehicle in traveling at a target vehicle speed by controlling a reaction force that is applied to the accelerator pedal of the vehicle.
2. Description of the Related Art
Technologies have been available in the art for applying an additional reaction force from a motor, in addition to the reaction force from a return spring, to the accelerator pedal of a vehicle (see Japanese Laid-Open Patent Publication No. 2003-260951 and U.S. Patent Application Publication No. 2003/0190996). According to Japanese Laid-Open Patent Publication No. 2003-260951, a threshold speed is calculated, and an additional reaction force is applied to the accelerator pedal when the speed of the vehicle reaches a threshold speed (see FIG. 2 and paragraph [0019] of the publication). Furthermore, according to Japanese Laid-Open Patent Publication No. 2003-260951, when the vehicle speed of the vehicle exceeds the threshold speed, a drive force of the rotating motor (2) is increased. A characteristic by which the drive force is applied (see FIG. 2 of the publication) is set depending on road conditions (see paragraphs [0019] through [0022] and FIGS. 3 through 5 of the publication).
According to U.S. Patent Application Publication No. 2003/0190996, a pedal reaction force (RP1), which acts on the accelerator pedal, is generated by an electric motor depending on a pedal depression amount (PS) (see FIG. 3 of the application). Furthermore, according to U.S. Patent Application Publication No. 2003/0190996, the reaction force is canceled when it is detected that the driver intends to accelerate the vehicle, for example, by depressing the accelerator pedal.
When the reaction force is reduced based on the driver's intention to accelerate the vehicle, since the accelerator pedal quickly becomes lighter as a result of being released from the reaction force, the driver possibly could depress the accelerator pedal more deeply than intended. According to Japanese Laid-Open Patent Publication No. 2003-260951 and U.S. Patent Application Publication No. 2003/0190996, therefore, the speed of the vehicle cannot be increased gradually.